Moyuan Cao

Bio-Inspired Titanium Dioxide Materials with Special Wettability and Their Applications

Their Applications Kesong Liu,†,∥ Moyuan Cao,† Akira Fujishima, and Lei Jiang*,†,‡ †Key Laboratory of Bio-Inspired Smart Interfacial Science and Technology of Ministry of Education, School of Chemistry and Environment, Beihang University, Beijing 100191, PR China ‡Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, PR China Research Institute for Science and Technology, Photocatalysis International Research Center, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan Institute for Superconducting and Electronic Materials, University of Wollongong, Innovation Campus, Squires Way, North Wollongong, NSW 2500, Australia

Floatable, Self-Cleaning, and Carbon-Black-Based Superhydrophobic Gauze for the Solar Evaporation Enhancement at the Air–Water Interface

Efficient solar evaporation plays an indispensable role in nature as well as the industry process. However, the traditional evaporation process depends on the total temperature increase of bulk water. Recently, localized heating at the air-water interface has been demonstrated as a potential strategy for the improvement of solar evaporation. Here, we show that the carbon-black-based superhydrophobic gauze was able to float on the surface of water and selectively heat the surface water under irradiation, resulting in an enhanced evaporation rate. The fabrication process of the superhydrophobic black gauze was low-cost, scalable, and easy-to-prepare. Control experiments were conducted under different light intensities, and the results proved that the floating black gauze achieved an evaporation rate 2-3 times higher than that of the traditional process. A higher temperature of the surface water was observed in the floating gauze group, revealing a main reason for the evaporation enhancement. Furthermore, the self-cleaning ability of the superhydrophobic black gauze enabled a convenient recycling and reusing process toward practical application. The present material may open a new avenue for application of the superhydrophobic substrate and meet extensive requirements in the fields related to solar evaporation.

Hydrophobic/Hydrophilic Cooperative Janus System for Enhancement of Fog Collection.

Harvesting micro-droplets from fog is a promising method for solving global freshwater crisis. Different types of fog collectors have been extensively reported during the last decade. The improvement of fog collection can be attributed to the immediate transportation of harvested water, the effective regeneration of the fog gathering surface, etc. Through learning from the natures strategy for water preservation, the hydrophobic/hydrophilic cooperative Janus system that achieved reinforced fog collection ability is reported here. Directional delivery of the surface water, decreased re-evaporation rate of the harvested water, and thinner boundary layer of the collecting surface contribute to the enhancement of collection efficiency. Further designed cylinder Janus collector can facilely achieve a continuous process of efficient collection, directional transportation, and spontaneous preservation of fog water. This Janus fog harvesting system should improve the understanding of micro-droplet collection system and offer ideas to solve water resource crisis.

Bio-inspired humidity responsive switch for directional water droplet delivery

In nature, the fibrils of awns can make an open–close motion in response to humidity changes. Shorebirds can suck water droplets by the repeated open–close motion of the beaks. Through the fusion of these inspirations, we report a directional droplet delivery device in response to humidity. A hydrogel-actuated switch was fabricated through the integration of polyacrylic acid hydrogel, cellulose membrane and superhydrophilic copper wires. It can realize directional droplet delivery. In the open state, the droplet was propelled directionally towards the tip-site of the conical channel by virtue of the Laplace pressure difference. When the switch shifted to be closed and the channel turned into a parallel one, the droplet was pinned due to the disappearance of the Laplace pressure difference. The switch for directional liquid delivery can attract broad interest in the field of microfluidics, droplet manipulation, etc.

Bioinspired Ultrastrong Solid Electrolytes with Fast Proton Conduction along 2D Channels

Solid electrolytes have attracted much attention due to their great prospects in a number of energy- and environment-related applications including fuel cells. Fast ion transport and superior mechanical properties of solid electrolytes are both of critical significance for these devices to operate with high efficiency and long-term stability. To address a common tradeoff relationship between ionic conductivity and mechanical properties, electrolyte membranes with proton-conducting 2D channels and nacre-inspired architecture are reported. An unprecedented combination of high proton conductivity (326 mS cm-1 at 80 °C) and superior mechanical properties (tensile strength of 250 MPa) are achieved due to the integration of exceptionally continuous 2D channels and nacre-inspired brick-and-mortar architecture into one materials system. Moreover, the membrane exhibits higher power density than Nafion 212 membrane, but with a comparative weight of only ≈0.1, indicating potential savings in system weight and cost. Considering the extraordinary properties and independent tunability of ion conduction and mechanical properties, this bioinspired approach may pave the way for the design of next-generation high-performance solid electrolytes with nacre-like architecture.

Superhydrophobic helix: controllable and directional bubble transport in an aqueous environment

Manipulating air bubbles in an aqueous medium exhibits both scientific and technologic value in gas-collection, selective aeration, and pollutant disposal. Superhydrophobic substrates, known as underwater superaerophilic substrates, offer numerous opportunities to develop advanced gas controlling systems, arising from its strong affinity to air bubbles in water. Herein, we present a superhydrophobic helix that is able to achieve controllable and directional bubble delivery. In an aqueous environment, the bubble tends to stay on the summit of the helix structure and moves along with the helix rotation. The velocity of the bubble delivery can be facilely tuned in terms of the spacing length of the helix. Continuous bubble collection and delivery were realized by integrating the helix with a gas needle and anti-buoyancy transport of the air bubbles was demonstrated using a tilted superhydrophobic helix. Taking advantage of the bubble controllability, a bubble based micro-reaction of H2 and O2 was conducted depending on the special helix structure with two directionalities. This contribution should provide new ideas for the exploration of functional superwettability materials and promote the development of gas-involved multi-phase systems.

Soft-binding ligand-capped fluorescent CdSe/ZnS quantum dots for the facile labeling of polysaccharide-based self-assemblies

In this research, soft-binding aminopropanol (APP) was employed as an efficient ligand, for the transfer of as-prepared hydrophobic CdSe/ZnS quantum dots (QDs) into polar solvents. It was found that the ligands at the surface of the original QDs could be completely replaced by APP after a phase-transferring process which successfully maintained fluorescence properties and original morphology of the QDs. The resulting intermediate QDs were soluble in common polar organic solvents, such as dimethyl sulfoxide (DMSO), dimethyl formamide (DMF) and tetrahydrofuran (THF), and the soft-binding ligand could be easily removed by exposure to water. Taking advantage of the excellent solubility of the APP-capped QDs and the soft-binding characteristics of APP, a novel reaction-free method was investigated for the fluorescent labeling of polysaccharide-based micelles via encapsulation of the intermediate QDs. The incorporation of QDs had little effect on the size of the micelles and did not elevate their cytotoxicity. A photo-induced fluorescence enhancement effect was observed for the incorporated QDs, and the QD-labeled micelles could be used for cell imaging. The concept of soft-binding ligand capped QDs and the reaction-free fluorescent labeling method can be applied to a wide range of QD studies.

One-step transformation of highly hydrophobic membranes into superhydrophilic and underwater superoleophobic ones for high-efficiency separation of oil-in-water emulsions

Superhydrophilic membranes have drawn much attention owing to their outstanding anti-fouling performance and ultrahigh permeation flux for wastewater treatment and oil–water separation. Since most widely used polymer membranes have high intrinsic hydrophobicity, a universal approach for superhydrophilic modification is highly required. Yet, how to simply transform highly hydrophobic membranes into superhydrophilic ones is still a challenge. Herein, we develop a one-step and general strategy to achieve the hydrophobic-to-superhydrophilic transformation of commercial membranes on the basis of catechol chemistry, i.e., co-deposition of tannic acid (TA) and 3-aminopropyltriethoxysilane (APTES) in aqueous solution. Owing to the distinct adhesion properties of TA and the reaction between the oxidative product of TA and the hydrolysis product of APTES, hydrophilic and hierarchical layer-colloidal nanospheres can be in situ assembled on various highly hydrophobic membranes including polyvinylidene fluoride (PVDF), polypropylene (PP), polytetrafluoroethylene (PTFE), copper mesh, stainless steel wire, and nylon mesh. The resulting superhydrophilic membrane can realize high-efficiency separation of various oil-in-water emulsions.

Unidirectional water delivery on a superhydrophilic surface with two-dimensional asymmetrical wettability barriers

A superhydrophilic surface decorated with 2D hydrophobic water barriers is proven to be a potential platform for unidirectional liquid transport. Differing from the existing systems based on 3D micro-structures, this functional surface features a simplified structure and high adaptiveness that provide more possibilities for the development of fluid manipulating materials.

Bioinspired Pressure-Tolerant Asymmetric Slippery Surface for Continuous Self-Transport of Gas Bubbles in Aqueous Environment

Biosurfaces with geometry-gradient structures or special wettabilities demonstrate intriguing performance in manipulating the behaviors of versatile fluids. By mimicking natural species, that is, the cactus spine with a shape-gradient morphology and the Picher plant with a lubricated inner surface, we have successfully prepared an asymmetric slippery surface by following the processes of CO2-laser cutting, superhydrophobic modification, and the fluorinert infusion. The asymmetric morphology will cause the deformation of gas bubbles and subsequently engender an asymmetric driven force on them. Due to the infusion of fluorinert, which has a low surface energy (∼16 mN/m, 25 °C) and an easy fluidic property (∼0.75 cP, 25 °C), the slippery surface demonstrates high adhesive force (∼300 μN) but low friction force on the gas bubbles. Under the cooperation of the asymmetric morphology and fluorinert infused surface, the fabricated asymmetric slippery surface is applicable to the directional and continuous bubble delivery in an aqueous environment. More importantly, due to the hard-compressed property of fluorinert, the asymmetric slippery surface is facilitated with distinguished bubble transport capability even in a pressurized environment (∼0.65 MPa), showing its feasibility in practical industrial production. In addition, asymmetric slippery surfaces with a snowflake-like structure and a star-shaped structure were successfully fabricated for the real-world applications, both of which illustrated reliable performances in the continuous generation, directional transportation, and efficient collection of CO2 and H2 microbubbles.